Konsekvensen er stor.

Er is the present tense of å være, which means to be.

So:

• å være = to be
• er = is / am / are depending on the subject

In this sentence, Konsekvensen er stor, er means is.

The ending -en makes the noun definite singular.

• en konsekvens = a consequence
• konsekvensen = the consequence

In Norwegian, the definite article is often attached to the end of the noun instead of being a separate word like English the.

Because the sentence is talking about a specific consequence, not just any consequence.

So the sentence means the consequence is ..., not a consequence is ....

This usually implies that the consequence is already known from the context, or has just been mentioned.

Compare:

• En konsekvens er stor = A consequence is large/major
  This is grammatically possible, but much less natural in most contexts.
• Konsekvensen er stor = The consequence is large/major
  This sounds like you are referring to a particular consequence already under discussion.

Because stor comes after er, so it is a predicative adjective, not an adjective directly attached to the noun.

In Norwegian, predicative adjectives usually agree with gender and number, but not with definiteness.

So:

• en konsekvens → stor
• et problem → stort
• konsekvensene → store

That gives:

• Konsekvensen er stor = singular common gender
• Problemet er stort = singular neuter
• Konsekvensene er store = plural

But if the adjective stands before a definite noun, then you do use the definite/plural-style form:

• den store konsekvensen = the big/major consequence

So:

• Konsekvensen er stor
• den store konsekvensen

Both are correct, but the grammar is different.

In Bokmål, konsekvens is normally a common-gender noun.

That means its basic article is:

• en konsekvens

And that is why the adjective form here is:

• stor, not stort

If it were a neuter noun, you would expect et in the indefinite form and -t on the adjective in this kind of sentence.

Not necessarily. Stor often literally means big, but with abstract nouns it can mean things like:

• major
• great
• serious
• significant
• considerable

So in a sentence like Konsekvensen er stor, stor is probably being used in an abstract sense, not to describe physical size.

Yes. It follows a very common pattern:

subject + verb + adjective

Here:

• Konsekvensen = subject
• er = verb
• stor = subject complement / predicative adjective

This is very similar to English:

• The consequence is large/major

If you want to talk about more than one consequence, you use:

• Konsekvensene er store = The consequences are great/major

Here both the noun and the adjective change:

• konsekvensen = the consequence
• konsekvensene = the consequences
• stor = singular common gender
• store = plural

To make it negative, put ikke after the verb:

• Konsekvensen er ikke stor. = The consequence is not great/major.

To make it a yes/no question, put the verb first:

• Er konsekvensen stor? = Is the consequence great/major?

This is a very common pattern in Norwegian.

Yes, but it does not mean exactly the same thing.

• Konsekvensen er stor = The consequence is great/major.
  This refers to a specific consequence already known in the conversation.

• Det er en stor konsekvens = That is a big/major consequence or It is a major consequence.
  This presents it more as a description or evaluation, often introducing the noun phrase rather than referring back to an already established one.

So the two sentences are related, but they are used in slightly different situations.

A simple learner-friendly approximation is:

kohn-seh-KVENS-en ehr stor

A few helpful points:

• The stress falls on -kvens-: konseKVENSen
• r is pronounced, though the exact sound depends on dialect
• stor has a long vowel

Pronunciation varies across Norway, so it is best to learn the local or standard pronunciation you are studying, but the stress pattern above is the important part to notice.